1. Field of the Invention
The present invention relates to a low-temperature liquefied gas outflow device, and more particularly to a low-temperature liquefied gas outflow device which can control the flow rate of a low-temperature liquefied gas such as liquid nitrogen.
2. Description of the Prior Art
There are many fields in which it is necessary to provide a flow of low-temperature liquefied gas at an accurately constant rate.
In general, low-temperature liquefied gas is naturally of a high vaporability, and once vaporization occurs, the resultant gas mixes with the liquefied gas. Thus it is difficult to maintain an accurate flow of low-temperature liquefied gas at a constant rate. Accordingly it is desirable that such a low-temperature liquefied gas should be prevented from evaporation so that the liquefied gas flow is completely liquid.
Particularly when using a liquefied gas flow in the liquid state, it is desirable to minimize the evaporation of the liquefied gas even after it has flowed out of the outflow device.
In prior art outflow devices, a single through-hole is provided in a nozzle and the surface area of the low-temperature liquefied gas flowing out of the nozzle through-hole is made to be as small as possible.
In such a prior art outflow device, if the pressure inside the device is constant, for example if it is at atmospheric pressure, the outflow rate is determined by the liquid level (head) and the diameter of the nozzle hole. Accordingly, when both of the liquid level and nozzle hole diameter are fixed, the only control that be effected on the outflow rate of liquefied gas is the insertion of the tip of a needle valve into the nozzle hole so that the opening of the hole is adjusted by the degree of insertion of the needle valve.
This control is, however, very difficult with a nozzle hole having a relatively small diameter. Thus, the prior art outflow device cannot meet the requirement of varying the outflow rate readily according to its various uses.